This section provides background information related to the present disclosure which is not necessarily prior art.
Shock absorbers are used in conjunction with automotive suspension systems to absorb unwanted vibrations which occur during driving. To absorb the unwanted vibrations, shock absorbers are generally connected between the sprung portion (body) and the unsprung portion (suspension) of the automobile. A piston is located within a pressure tube of the shock absorber and the pressure tube is connected to one of the unsprung and sprung portions of the vehicle. The piston is connected to the other of the sprung portion and unsprung portion of the automobile through a piston rod which extends through the pressure tube. The piston divides the pressure tube into an upper working chamber and a lower working chamber both of which are filled with hydraulic fluid. Because the piston is able, through valving, to limit the flow of the hydraulic fluid between the upper and the lower working chambers when the shock absorber is compressed or extended, the shock absorber is able to produce a damping force which counteracts the vibration which would otherwise be transmitted from the unsprung portion to the sprung portion of the vehicle. In a dual-tube shock absorber, a fluid reservoir or reserve chamber is defined between the pressure tube and a reserve tube. A base valve is located between the lower working chamber and the reserve chamber to also produce a damping force which counteracts the vibrations which would otherwise be transmitted from the unsprung portion of the vehicle to the sprung portion of the automobile.
As described above, for a dual-tube shock absorber, the valving on the piston limits the flow of damping fluid between the upper and lower working chambers when the shock absorber is extended to produce a damping load. The valving on the base valve limits the flow of damping fluid between the lower working chamber and the reserve chamber when the shock absorber is compressed to produce a damping load. During driving, the suspension system moves in jounce (compression) and rebound (extension). During jounce movements, the shock absorber is compressed causing damping fluid to move through the base valve in a dual-tube shock absorber. A damping valve located on the base valve controls the flow of damping fluid and thus the damping force created. During rebound movements, the shock absorber is extended causing damping fluid to move through the piston in the dual-tube shock absorber. A damping valve located on the piston controls the flow of damping fluid and thus the damping force created.
In a dual-tube shock absorber, the piston and the base valve both normally include a plurality of compression passages and a plurality of extension passages. During jounce (compression) movements in a dual-tube shock absorber, the damping valve or the base valve opens the compression passages in the base valve to control fluid flow and produce a damping load. A check valve on the piston opens the compression passages in the piston to replace damping fluid in the upper working chamber but this check valve may or may not contribute to the damping load. The damping valve on the piston closes the extension passages of the piston and a check valve on the base valve closes the extension passages of the base valve during a compression movement. During rebound (extension) movements in a dual-tube shock absorber, the damping valve on the piston opens the extension passages in the piston to control fluid flow and produce a damping load. A check valve on the base valve opens the extension passages in the base valve to replace damping fluid in the lower working chamber but this check valve may or may not contribute to the damping load.
Prior art double tube shock absorber structure is built by using a steel reserve tube. The prior art pressure tube has a thin wall thickness just to hold and guide valving elements. Double tube steel construction is heavy and requires a painting process to fulfill corrosion requirements. Painting processes bring contamination issues and can negatively influence manufacturing costs. Prior art shocks require a base valve assembly arc welding and a rolling process for closing of the reserve tube. Arc welding is a process with high energy consumption and is a source of contamination. Roll closing imposes a need for a high strength rod guide and an oil seal washer.